Swift 2.0异常处理 [英] Swift 2.0 exception handling

问题描述

我们想知道SWIFT中的整个代码块的错误处理机制。

We want to know error handling mechanism in SWIFT for whole block of code.

正如swift中有一些用于错误处理的技术，其中一些就像使用 guard 或如果让。还可以使用 do-catch 语句来实现。但是我们正在处理 使用单个try-catch块 的错误，正如我们在 Objective-C 。在 Objective-C 中，该块很容易处理任何代码行中的错误。所以我们想知道这种类型的机制。

As, in swift, there are some techniques used for error handling, some of them are like using guard or if let. Also we can achieve it using do - catch statement. But we are getting stuck while handling error for whole bunch of code using single try-catch block as we were doing in Objective-C. In Objective-C this block was easily handling errors within any line of code in it. So we want to know this type of mechanism in swift.

现在，我们知道如果我们需要处理错误，那么使用 guard ， if-let 语句，或者写一些自定义的方法，将抛出错误，并在 do-catch 块中使用该方法。那么Swift中是否有任何机制将与 try-catch 块平行，就像在 Objective-C 中一样，所以我们不需要为整条代码中的每一行代码写入 if-let 或 guard 语句

For now, we came to know that if we need to handle error, then use guard, if-let statement for each line, or write some custom methods which will throw the error and use that method in do-catch block. So is there any mechanism in Swift which will be parallel to try-catch block just like in Objective-C so we don’t need to write if-let or guard statement for each single line of code in that whole bunch of code.

这是我们如何使用 if-let 和 guard let for single line statement null处理：

This is how we used if-let and guard let for single line statement null handling :

if-let 实现示例代码片段： -

if-let implementation sample code snippet :-

if let title = dict["title"].string
{
   let myTitle = title
}

但下面提到我们想要在swift中解决问题的方案 try -catch 阻止代理功能。

But below is mentioned scenario in which we want solution in swift for try-catch block within delegate functions.

Objective-C 中的示例代码片段，使用 try-catch 块

A sample code snippet in Objective-C using try-catch block

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{

    @try {
        static NSString *itemIdentifier = @"CustomCell";
        //Some line of code where exception may occur…
        //Some line of code where exception may occur…
        //Some line of code where exception may occur…
        //Some line of code where exception may occur…
        //…
        //…
        //… 
        return cell;
    }
    @catch (NSException *exception) {
        NSLog(@"Exception in  cellForItemAtIndexPath - %@",exception.description);
    }
}

以上是我们在 Objective-C 但是现在我们想在Swift中使用同样的东西 try-catch ，但到现在为止我们还没有找到任何解决方案，那么我们如何处理这样的情况我们可以添加 try-catch 块来委托表视图，集合视图，...等功能。

Above is the code snippet which we were using in Objective-C. But now we want to use same thing of try-catch in Swift. But till now we haven’t found any solution. So how do we handle such scenario in which we can add the try-catch block to delegate functions of table view, collection view, ... , etc.

推荐答案

正如@JeremyP所说，快速的没有例外，为了使这个清楚，你可以使用一个 do-catch 阻止捕获多个错误，但是必须使用 if-let 和 guard 来避免致命错误不可捕获，例如：

As @JeremyP said, in swift there is no exceptions. To make this clear you can you can use a single do-catch block to catch multiple errors, nevertheless if-let and guard has to be used to avoid fatal errors which are not catchable. For example:

do {
  try method1()
  try method2()
} catch {
  // do something with the error 
}

但上一个例子不会处理致命错误，例如：

but the previous example won't handle a fatal error, for example:

do {
  try method1()
  let myVar = anOptionalVar!
} catch {

}

此代码不会处理一个致命的错误，如果aOptionalVar是 nil ，并强制解开它将导致一个致命的错误，将终止执行。

this code won't handle a fatal error, if anOptionalVar is nil and you force unwrap it this will cause a fatal error which will terminate execution.

所以@JeremyP描述的模式应该用于处理错误：

So the pattern described by @JeremyP should be used to handle errors:

enum myError: ErrorType {
  case BadError
}

do {
  guard let myVar = anOptionalVar else { throw MyError.BadError }
} catch MyError.BadError {
  // do something with the error
}

所以，从swift 2，没有办法使用 guard 和 if-let 保持安全，免于致命错误，您唯一的选择是使用它们并传播 ErrorType 。

So as of swift 2 there is no way around using guard and if-let to stay safe from fatal errors, your only option is using them and propagate an ErrorType instead.

这篇关于Swift 2.0异常处理的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！